A study on fibre addition to gluten free bread: its effects on bread quality and in vitro digestibility.

The aim of this study was to assess the impact of fibre addition on gluten-free (GF) dough properties and bread technological quality, and on protein and starch in vitro digestibility. Soluble (Inulin, In) and insoluble fibres (oat fibre, OF, and type IV resistant starch, RSIV) were used at 5 and 10% substitution levels. Dough firmness increased when insoluble fibres were added, and decreased when In was used. Incorporation of insoluble fibres resulted into bread with a low specific volume (SBV) since firmer dough were more difficult to expand during proofing and baking. Staling rate was reduced after fibre addition, with the exception being OF 10%, as its lower SBV may have favoured molecule re-association. In general, protein and starch digestibility increased when fibres were added at 5%, and then decreased after further increasing the level. Fibres may have disrupted bread crumb structure, thus increasing digestibility, although the higher addition may have led to a physical and/or chemical impediment to digestion. Inulin has well-known physiological effects, while RS presented the most important effect on in vitro starch digestibility (GI). These results showed the possibility of adding different fibres to GF bread to decrease the GI and increase protein digestibility, while obtaining an overall high quality end-product.

Effect of four types of dietary fiber on the technological quality of pasta.

The development of dietary fiber-enriched foods permits to obtain products with functional properties but can cause several problems in technological quality. The aim of this study was to study the quality of pasta obtained by replacing bread wheat flour with resistant starch II (RSII), resistant starch IV (RSIV), oat bran (OB) and inulin (IN) with the purpose of improving their nutritional quality. RSII, RSIV, OB and IN were substituted for a portion of bread wheat flour at levels 2.5%, 5.0%, 7.5% and 10.0%. Cooking properties, amylose and inulin losses, color and texture were measured. Finally, nutritional quality of enriched pasta was evaluated by protein losses during cooking and total dietary fiber. Microstructure of pasta was analyzed by scanning electron microscopy. Addition of RSII into pasta formulation improved the quality of the final product. RSIV-enriched pasta presented an improvement in textural characteristics and OB affected cooking properties positively up to 5% of substitution. Inulin was lost during cooking; besides, its addition negatively affected the technological quality of pasta. The results obtained in this study prove that it is possible to elaborate pasta with acceptable cooking quality and with improved nutritional characteristics by adding 10% of RSII and RSIV and 5% of OB.